The invention relates to a fuel-operated vehicle heater, especially an auxiliary heater.
Such a heater generally has a nozzle, sitting on a nozzle holder, to which fuel is fed from a fuel line, via a filter, a fuel pump and a solenoid valve. A fuel mixture is produced in the area of the nozzle outlet from the fuel and combustion air which is delivered by a combustion air blower driven by a drive motor. To ignite this mixture, an ignition spark emitter is placed so that free ends of its ignition electrodes are directed into proximity with the nozzle outlet. Optionally, the nozzle holder carries a preheater and is supported by a flange on the housing of the heater.
In the case of heaters of this type (for example, the Type DBW 2010 heater produced by the assignee of the present application), up to now the components, such as the nozzle holder with the nozzle, the fuel pump, filter, solenoid valve and ignition spark emitter were assembled separately in the heater with the necessary connections.
As a result, not only is assembly of such a heater time-consuming but connection mistakes can occur by confusion. Further, in the case of present heaters, the functioning units necessary for the burner occupy a relatively large amount of space, so that the heater, as a whole has rather large installation dimensions.
Therefore, a primary object of the invention is to overcome the difficulties described above and to achieve a fuel-operated heater of the noted type which is as compact as possible and enables a substantially simplified assembly of the heater to be obtained. Also, it is a further object to enable the power consumption of the units needed for operation of the heater to be reduced as much as possible.
According to a preferred embodiment, especially the nozzle holder, fuel pump, filter and solenoid valve are combined in a single subassembly, which may be handled as a unit. This subassembly is designed to be extremely compact and forms the central operating unit of the burner of such a fuel-operated heater. Assembly of the heater is substantially simplified by the fact that, in this subassembly, several functional parts are combined and, thus, only the subassembly needs to be attached at predetermined places, for example, with the aid of screws.
Furthermore, it has been shown, in a surprising way, that by this compact type of construction of the heater in connection with the arrangement of the parts necessary for functioning, the heater can operate with less noise than before, and, also, a reduction of the power consumption is attained.
In an advantageous further development of the invention, the filter is joined with the fuel pump, so that the filter forms a combined functional and support subassembly with the fuel pump. As a result, a further considerable saving of space is achieved. Further, in the combustion operation, because of its closeness to the combustion chamber, the filter is heated to the extent that paraffin precipitation is avoided in the case of cold fuel.
Preferably, the ignition spark emitter with integrated electrodes can be fastened onto the above indicated subassembly formed according to the invention, so that no particular cables are needed for the ignition spark emitter, as a result of which assembly is made easier and a change of polarity is no longer possible. Further, because of the absence of the cables, especially for the ignition electrodes, the degree of supression of the ignition noise (HF region) can be considerably improved.
Advantageously, the subassembly is fastened to a flange of the heater housing, for which screws or the like can be provided, and the flange with the subassembly fastened thereto is then placed in a receiving space of the heater in a predetermined way.
According to another advantageous feature according to the invention, the housing flange is used not only for holding and supporting the subassembly but also the feed line and return line running to the fuel pump are designed in the flange and are formed, for example, by bores going through the flange. Thus, separate fuel lines running to and from the fuel pump (as have been customary) can be eliminated and the intrinsic safety of the heater improved. In this way, also, the assembly operation is made easier. Further, in a constructively very simply way, a connection can be established from the feed line and return line in the flange to the fuel pump intake and/or output with the help of a seal. The seal, on the one hand, works with the corresponding connecting parts of the pump housing and, on the other hand, with the corresponding countersurfaces on the flange. Since the flange easily is heated during the combustion operation, the fuel is preheated, particularly in the feed line, and better combustion is attained.
For supplying electric power to the parts of the subassembly, advantageously, a central connecting device is provided with a control device or connecting device. This device is fastened to the side of the flange which faces away from the nozzle. In this way, additional electric connecting lines can be eliminated and the central connecting device largely replaces a cable assembly that has been the usual means for providing electrical power up to now. Since, in this way, mixing up of cables and the resulting connecting mistakes are avoided, yet another significant simplification of the assembly and a high operating reliability of the heater is attained.
To use the space around the nozzle holder and nozzle as much as possible, the fuel pump with the attached filter, the solenoid valve and the ignition spark emitter are placed radially around the nozzle holder, so that the smallest possible dimensions for the burner as a whole are attained.
Preferably, the fuel pump and the combustion air blower delivering the combustion air are driven directly, for which purpose the drive motor is fastened to the side of the flange that faces away from the nozzle. By having the fuel pump and combustion air blower directly driven, power losses on the drive side are reduced and, especially, the design of the drive side of such a heater is simplified.
The heater according to the invention is also so constituted that, for different power ranges of the heater, only the nozzle and drive motor have to be exchanged. All other parts can be kept unchanged for different heating power ranges, so that, in regard to warehousing, a smaller inventory expenditure is required than heretofore has been necessary. Thus, the heater according to the invention also can be favorably adjusted to different heating ranges from a production engineering standpoint in an economical way.
Advantageously, a preheater in the form of a heating cartridge is also integrated into the subassembly. To this end, the nozzle holder can be provided with a projection, which has a through-hole, into which the preheater cartridge may be plugged. Preferably, the preheater is placed close to the filter so that, during operation of the preheater, the filter is also heated to prevent paraffin precipitation on the filter at low temperatures.
Preferably, an O-ring seal is provided for sealing of the connection between the fuel pump of the subassembly and the mounting flange of the heater housing so that, as a result of the design of the fuel supply in the flange, there are few places requiring sealing. In this way, the operating safety of such a heater is increased.
Further, the design according to the invention is also such that the solenoid valve is in the immediate proximity of the atomizing nozzle, so that there is a extremely short fuel path between the solenoid valve and the atomizing nozzle. Thus, with closing of the solenoid valve, a continued dripping of fuel from the atomizing nozzle is largely prevented.
Additionally, the burner according to the invention has the pump and, especially, the filter facing toward the combustion space of the heater. Therefore, a more favorable operating behavior results, particularly at low temperatures, since these parts are heated during combustion operation and thereby clogging of the filter, for example, by paraffin precipitation, is prevented.
Still a further aspect of the invention lies in the subassembly, made of the nozzle holder, fuel pump, filter and solenoid valve as well as optionally also the preheater, also holding a flame monitor. For this purpose, a socket opening is formed in the subassembly in which a phototransistor can be plugged in as flame monitor.
In the atomizing burner according to the invention, therefore, the subassembly unit which holds and contains all the essential components necessary for the functioning of a burner.
For an energy-saving operation of the preheater, such as the heating cartridge, the preheater is not always switched on for the same amount of time, but rather the switch-on period is varied, namely, it is shorter the higher the temperature of the heater. Advantageously, the time variation takes place in steps as a function of predetermined temperature threshold values. By means of a timing circuit between a temperature sensor, such as a water temperature sensor in the case of a water heater, and the preheater, the preheater switch-on period can be so varied that, as a function of the temperature threshold values, in each case it changes an integral multiple of a minimum switch-on period of about one minute. Since, hereby, in comparison with a constant specified switch-on period of the preheater, the power consumption can be considerably reduced, the preheater consumes less energy for operation than up to now, and the preheater can even be cut off if the temperature condition of the heater makes preheating unnecessary.
These and further objects, features and advantages of the present invention will become more obvious from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, a single embodiment in accordance with the present invention.